Plasma display device

ABSTRACT

Disclosed is a plasma display device that provides high luminance and minimal degradation in luminance under panel operations. A blue phosphor in a phosphor layer has a crystal structure of MeMgSi 2 O 6 :Eu or Me 3 MgSi 2 O 8 :Eu (where, Me contains at least one of Ca, Sr, and Ba) produced with a precursor that is obtained by any one of methods: an aqueous solution synthesis method, a spray synthesis method, a hydrothermal synthesis method, and a hydrolysis method. The phosphor has an average particle diameter ranging from 0.1 to 3.0 μm.

TECHNICAL FIELD

The present invention relates to a plasma display device for displayingimages on a television or other equipment.

BACKGROUND ART

In color display devices employed for image display on computers or TVs,a plasma display device having a plasma display panel (hereinafterreferred to as a PDP) has recently received considerable attention as acolor display device with large sized screen but lightweight body due toits low-profile structure.

A PDP displays images in full color by performing an additive colorprocess on red, green, and blue—known as the three primary colors. Torealize the full color display, the PDP has phosphor layers that arerespectively prepared for emitting red (R), green (G), and blue (B) ofthe three fundamental colors. A phosphor layer is formed of phosphorparticles. The phosphor particles are excited by ultraviolet raysgenerated in a discharge cell in the PDP, so that visible lights of red,green, and blue are produced.

As the well-known chemical compounds for the phosphors above are: (Y,Gd)BO₃:Eu³⁺, Y₂O₃:Eu³⁺ for emitting red; Zn₂SiO₄:Mn²⁺ for emitting green;and BaMgAl₁₀O₁₇:Eu²⁺, CaMgSi₂O₆:Eu for emitting blue. Each phosphor ismanufactured through solid phase reaction; after mixed predeterminedmaterial, it is baked at high temperature beyond 1000° C. (for example,see Phosphor Handhook, pp 219 and 225, Ohmsha). Because the bakingprocess sinters the phosphor particles, they should be crushed to aproper size before using: an average particle diameter of 2-5 μm for thered, and the green phosphors, 3-10 μm for the blue phosphor.

The prior-art phosphors above, however, have a problem—particularly inthe blue phosphor formed of BaMgAl₁₀O₁₇:Eu, phosphor luminance decreasesin the heating step of the phosphor layer-forming process or under paneloperation. Employing the crystal structure of CaMgSi₂O₆:Eu system as theblue phosphor can slightly improve in the phosphor luminance in theheating step of the phosphor layer-forming process or in paneloperation; however, the manufacturing method and the crystal structureby the conventional solid phase reaction has been facing the problem oflow luminance—especially under panel operation, serious degradation inluminance occurs. The inconvenience comes from the fact that the blueemitting phosphor with the crystal structure of CaMgSi₂O₆:Eu is easy toundergo sintering, due to its low melting point, in the solid phasereaction. Therefore, there is no way, without crushing, to obtain a bluephosphor particle having the diameter less than 8 μm. In the solid phasereaction, the crystal of CaMgSi₂O₆:Eu as the phosphor should preferablybe sintered at temperatures around 1400° C.; however, such a hightemperature accelerates particle growth, allowing each particle to havea particle diameter of several ten μm. When the structure with a largeparticle diameter due to the sintering is crushed to obtain a particlediameter less than 3 μm, a structural defect developed in the crystalseriously impairs the luminance. The problem above has been an obstacleto realizing an improved panel having high luminance and minimizingluminance degradation under panel operation. The problem above alsoshortens the lifetime of the panel.

The present invention addresses the inconvenience above. It is thereforethe object to obtain the blue emitting phosphor with high luminance.Also, it is another object to provide a panel that can minimizedegradation in luminance.

DISCLOSURE OF THE INVENTION

To achieve the aforementioned object, the plasma display device of thepresent invention has a structurally improved blue-emitting phosphorhaving an average particle diameter ranging from 0.1 to 3.0 μm. And morespecifically, the phosphor for blue emission has a structure ofMeMgSi₂O₆:Eu or Me₃MgSi₂O₈:Eu (where, Me is a mixture of at least one ofCa, Sr, and Ba) produced with a precursor that is obtained by any one ofthe following methods: an aqueous solution reaction synthesis method, aspray synthesis method, a hydrothermal synthesis method, and ahydrolysis method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a plasma display panel, with a front glasssubstrate removed, in accordance with an embodiment of the presentinvention.

FIG. 2 is a perspective view illustrating the structure of the imagedisplay area of the plasma display panel of the embodiment.

FIG. 3 is a block diagram of the plasma display device of theembodiment.

FIG. 4 is a sectional view illustrating the structure of the imagedisplay area of the plasma display panel of the embodiment.

FIG. 5 is a schematic view illustrating the structure of an ink applyingdevice, which is used in a phosphor layer-forming process in the presentinvention.

DETAILED DESCRIPTION OF CARRYING OUT OF THE INVENTION

An exemplary embodiment of the plasma display device according to thepresent invention is described hereinafter with reference to theaccompanying drawings.

FIG. 1 is a schematic plan view of a plasma display panel (PDP), with afront glass substrate removed, in accordance with an embodiment of thepresent invention. FIG. 2 is a perspective view of the PDP, showing apart of an image display area in section. In FIG. 1, the number ofdisplay electrodes, display scan electrodes, and address electrodes isreduced for sake of clarity.

In FIG. 1, PDP 100 contains front glass substrate 101 (not shown), rearglass substrate 102, N display electrodes 103, N display scan electrodes104 (where a parenthesized N indicates the Nth electrode), M addresselectrode 107 (where a parenthesized M indicates the Mth electrode), andhermetic seal layer 121. The PDP has an electrode matrix having athree-electrode structure made of respective electrodes 103, 104, and107. Cells are formed at the respective intersections of display scanelectrodes 104 and address electrodes 107. Reference numeral 123indicates an image display area.

PDP 100 has, as shown in FIG. 2, front glass substrate 101, and rearglass substrate 102 facing to substrate 101. The two substrates formdischarge space 122 therebetween, which is filled with a discharge gas.On a principle surface of front glass substrate 101, display electrodes103, display scan electrodes 104, dielectric glass layer 105, and MgOprotective layer 106 are disposed. On the other hand, disposed on aprinciple surface of rear glass substrate 102 are address electrodes107, dielectric glass layer 108, barrier ribs 109, and phosphor layers110 (R, G, B). Such structured PDP is connected to a driver circuit toform a plasma display device.

When an image is displayed on the plasma display device, first, displaydriver circuit 153, display scan driver circuit 154, and address drivercircuit 155—the three circuits form driver circuit 150—are connected toPDP 100, as shown in FIG. 3. Next, according to the control ofcontroller 152, a voltage is applied across display scan electrode 104and address electrode 107 of a cell to be lit for address dischargetherebetween. Then, a pulse voltage is applied across display electrode103 and display scan electrode 104 for sustain discharge. The sustaindischarge generates ultraviolet light in the cell. The phosphor layersexcited by the ultraviolet light emit light, thereby lighting the cell.In this way, combination of lit and unlit cells of the respective colorsproduces an image on the display.

Now will be described a method of manufacturing the aforementioned PDPwith reference to FIGS. 1 and 2.

First, N display electrodes 103 and N display scan electrodes 104 arearranged on front glass substrate 101 alternately, parallel to eachother, like stripes. (In FIG. 2, only two of respective electrodes areshown for simplicity.) Thereafter, the electrodes are covered withdielectric glass layer 105, and further over which, MgO protective layer106 is formed.

Display electrodes 103 and display scan electrodes 104 are made ofsilver. These electrodes are formed by applying a silver paste forelectrodes by screen printing and then baking the paste.

Dielectric glass layer 105 is formed by applying a paste containing leadglass material by screen printing, and baking the paste at apredetermined temperature for a predetermined period of time (e.g. at560° C. for 20 min.) to obtain a desired thickness (approx. 20 μm). Asfor the paste containing lead glass material, a mixture of PbO (70 wt%), B₂O₃ (15 wt %), SiO₂ (10 wt %), Al₂O₃ (5 wt %) and an organic binder(α-terpineol containing 10% of ethyl cellulose dissolved therein) isoften used. The aforementioned organic binder contains a resin dissolvedin an organic solvent. Acrylic resin can be used as a resin other thanthe ethyl cellulose, and n-butylcarbitol as an organic solvent. Further,a dispersant—for, example, glyceryl trileate—can be mixed into such anorganic binder.

MgO protective layer 106 is made of magnesium oxide (MgO). The layer isformed into a predetermined thickness (approx. 0.5 μm) by sputtering orchemical vapor deposition (CVD) method.

Now, the explanation turns to the rear panel. First, M addresselectrodes 107 are formed in lines on rear glass substrate 102 by screenprinting a silver paste and then baking the paste. Next, dielectricglass layer 108 is formed by applying a paste containing lead glassmaterial to the address electrodes by a screen printing. Further,barrier ribs 109 are formed by repeatedly applying the same pastecontaining lead glass material to the dielectric glass layer at apredetermined pitch by screen printing and thereafter baking the paste.These barrier ribs 109 divide, in the direction of the lines, dischargespace 122 into respective cells (i.e., unit emission area).

FIG. 4 is a partially sectional view of PDP 100. As shown in FIG. 4,interval dimension W between barrier ribs 109 is determined to a valueranging from approx. 130 to 240 μm, according to a high definitiontelevision (HD-TV) screen having a diagonal size ranging from 32 to 50in.

Red (R) and green (G) phosphor particles are prepared by a hydrothermalsynthesis method, and blue (B) phosphor particles are prepared by ahydrothermal synthesis method, atomization synthesis method, orhydrolysis method. Paste-like phosphor ink made of red (R), green (G),or blue (B) phosphor particles and an organic binder is applied togrooves between barrier ribs 109, and baked at temperatures ranging from400 to 590° C. to burn out the organic binder. As a result, phosphorlayers 110—in which phosphor particles of corresponding colors are boundwith each other—are formed.

It is preferable that thickness L in the direction of lamination ofphosphor layers 110 on address electrode 107 is approx. 8 to 25 timesthe average diameter of phosphor particles of each color. That is, inorder to constantly achieve a certain luminance (emission efficiency)when a phosphor layer is irradiated with an amount of ultraviolet light,the phosphor layer needs to absorb ultraviolet light generated in thedischarged space, not allowing to pass therethrough. For this purpose,it is desirable that the phosphor layer has a thickness formed of atleast eight layered-, preferably, approx. 20 layered-phosphor particles.Having a thickness beyond 20-layered lamination almost “saturates”emission efficiency—this is because sufficiently large discharge space122 cannot be ensured due to the thickened layer. Phosphor particleshaving preferably small diameters and spherical shapes, like thoseobtained by hydrothermal synthesis, atomization synthesis, hydrolysismethods, have a packing factor of the phosphor layer and a total surfacearea of the phosphor particles larger than those of phosphor particleshaving non-spherical shapes, even when the number of laminated layersare the same. As a result, phosphor particles having spherical shapesincrease the surface area contributing to actual light emission of thephosphor layer, thereby enhancing the emission efficiency. The synthesismethod of phosphor layers 110 and the phosphor particles employed forthe phosphor layers will be described later.

The front panel and the rear panel produced in this manner are placedone on the other so that the respective electrodes on the front panelare orthogonal to the address electrodes on the rear panel. Sealingglass is inserted between the panels along the periphery thereof andbaked, for example, at temperatures of approx. 450° C. for 10 to 20 min.to form hermetical seal layer 121 for sealing. Next, discharge space 122is once evacuated to a high vacuum (e.g. 1.1×10⁻⁴ Pa) and filled with adischarge gas, namely, He—Xe or Ne—Xe inert gas, at a predeterminedpressure, to complete PDP 100.

FIG. 5 is a schematic diagram showing the structure of an ink dispenserused in forming phosphor layers 110. As shown in FIG. 5, ink dispenser200 includes server 210, pressure pump 220, and header 230. Phosphor inkis pressurized by pressure pump 220 and supplied from server 210, whichstores the phosphor ink, to header 230. Header 230 contains ink chamber230 a and nozzle 240. The phosphor ink, which was fed to ink chamber 230a with application of pressure, is continuously ejected from nozzle 240.It is desirable that bore diameter D of nozzle 240 is sized at least 30μm to prevent clogging of the nozzle. It is also desirable that borediameter D is equal to or smaller than interval W between barrier ribs109 (approx. 130 to 200 μm) to properly apply the ink to the groovebetween the barrier ribs. Hence, bore diameter D is usually determinedto 30 to 130 μm.

Header 230 is structured to be driven linearly by a header scanningmechanism (not shown). Continuously ejecting phosphor ink 250 fromnozzle 240 while scanning header 230 allows phosphor ink to be uniformlyapplied to the grooves between baffler ribs 109 on rear glass substrate102. Viscosity of the phosphor ink is kept within the range of 1500 to30000 centipoises (CP) at a temperature of 25° C.

This server 210 also has a mixer (not shown). Mixing preventsprecipitation of particles in phosphor ink. Header 230 is integrallyformed with ink chamber 230 a and nozzle 240 by performing machining andelectric discharge machining on a metallic material.

For the reader's convenience, the following is a list of the referencenumbers which are set forth in the figures together with theirdefinition according to the foregoing description:

-   100: PDP-   101: front glass substrate-   102: rear glass substrate-   103: display electrodes-   104: display scan electrodes-   105: dielectric glass-   106: MgO protective layer-   107: address electrodes-   108: dielectric glass layer-   109: barrier ribs-   110R: phosphor layer (Red)-   110G: phosphor layer (Green)-   110B: phosphor layer (Blue)-   122: discharge space-   200: ink dispenser-   210: server-   220: pressure pump-   230: header-   230 a: ink chamber-   240: nozzle-   250: phosphor ink

Forming phosphor layers is not limited to the aforementioned method;other various kinds of methods, such as photolithography, screenprinting, and a method of disposing a film including phosphor particlesmixed therein, can be employed.

The phosphor ink is prepared by mixing phosphor particles with eachcolor, a binder, and a solvent so that the mixture has a viscosityranging 1,500 to 30,000 centipoises (CP). A surface active agent,silica, a dispersant in amount of 0.1 to 5 wt % can also be added, asrequired.

As a red phosphor included in this phosphor ink, a compound representedby (Y, Gd)_(1−x)BO₃:Eu_(x) or Y_(2−x)O₃:Eu_(x) is used. In thesecompounds, the element Eu substitutes for a part of the element Yconstituting the matrix of the compounds. It is preferable that thesubstitution value X of the element Eu with respect to the element Y is0.05≦X≦0.20. Having X larger than 0.20 invites serious degradation inluminance in spite of achieving a high luminance. For this reason, sucha red phosphor is unlikely to be practical. On the other hand, having Xsmaller than 0.05 lowers the composition ratio of Eu mainly emittinglight, accordingly decreasing the luminance. The phosphor with decreasedluminance can no longer serve as a phosphor.

As a green phosphor, a compound represented by Ba_(1−x)Al₁₂O₁₉:Mn_(x) orZn_(2−x)SiO₄:Mn_(x) is used. Ba_(1−x)Al₁₂O₁₉:Mn_(x) is a compound inwhich the element Mn substitutes for a part of the element Baconstituting the matrix of the compound. Zn_(2−x)SiO₄:Mn_(x) is acompound in which the element Mn substitutes for a part of the elementZn constituting the matrix of the compound. For the same reason asdescribed in the case of the red phosphor, it is preferable that thesubstitution value X of the element Mn with respect to the element Ba orZn is 0.01≦X≦0.10.

As a blue phosphor, a compound represented by Me_(1−x)MgSi₂O₆:Eu_(x) orMe_(3(1−x))MgSi₂O₈:Eu_(x)—where, Me is a mixture of at least one of Ca,Sr, and Ba— is used. Me_(1−x)MgSi₂O₆:Eu_(x) andMe_(3(1−x))MgSi₂O₈:Eu_(x) are compounds in which the element Eusubstitutes for a part of the element Me(Ca, Sr, Ba) constituting thematrix of the compounds. Again for the same reason described in the red,and the green phosphors, the substitution value X of the element Eu withrespect to the element Me should preferably be 0.03≦X≦0.2.

The each phosphor described above is a phosphor (with no grindingprocess), which is manufactured with a precursor obtained through anaqueous solution reaction method, hydrothermal synthesis method,atomization baking method, or hydrolysis method. These methods ofmanufacturing phosphors will be explained later.

Ethyl cellulose or acrylic resin can be used as a binder included inphosphor ink (in an amount of 0.1 to 10 wt % of the ink). α-terpineol orn-butylcarbitol can be used as a solvent. Polymers, such as PMA and PVA,can also be used as a binder. As for solvent, organic solvent, such asdiethyleneglycol and methyl ether, can also be used.

According to the embodiment, first, a precursor for a phosphor isprepared in an aqueous solution. With the precursor, the embodimentemploys a hydrothermal synthesis method, atomization synthesis method,hydrolysis method to manufacture a phosphor particle. Hereinafter willbe described an example of the manufacturing methods. The aforementionedmethod is a synthesis and crystal growth method, which providesspherical phosphor particles.

(1) Blue Phosphor

Here will be described Ca_(1−x)MgSi₂O₆:Eu_(x), which is known as a bluephosphor. In a mixed solution fabrication process, materials of thephosphor, i.e., barium nitrate [Ba(NO₃)₂], magnesium nitrate [Mg(NO₃)₃],silicon oxide [SiO₂]—colloidal silica, and europium nitrate [Eu(NO₃)₂]are mixed in a molar ratio of Ba(NO₃)₂:Mg(NO₃)₃:SiO₂:Eu(NO₃)₂=1−X:1:2:X(0.03≦X≦0.20). This mixture is dissolved in an aqueous medium to preparea mixed solution. Ion-exchange water or pure water is preferably usedfor the aqueous medium by virtue of its containing no impurities;however, an aqueous medium containing non-aqueous solvent (e.g. methanoland ethanol) can also be used.

Next, an alkaline (basic) solution, such as potassium hydrate, is addedto the hydrate mixed solution prepared above to produce a hydrate (i.e.,a precursor) having spherical particles. The hydrate is put into acontainer made of a corrosion- and heat-resistant material, such as goldand platinum. Then, the hydrate is hydra-thermally synthesized in a highpressure vessel, using equipment capable of heating and pressurizing atthe same time, such as an autoclave, at specified temperatures (100 to300° C.) under specified pressures (0.2 to 10 MPa). In this case, analuminum powder or a graphite powder is used as a reducer for the bluephosphor. The hydrothermal synthesis is thus carried out for 12 to 20hours to obtain a spherical precursor.

Other than the aforementioned method with the use of autoclave pressure,a spray synthesis method can be used. In this case, the hydrate mixedsolution is directly fed from the pressure nozzle; the solution isultrasonically sprayed into a furnace heated at temperatures rangingfrom 1000 to 1500° C. to obtain the spherical precursor.

Next, the obtained precursor powder is baked in a reducing atmospherecontaining 5% of hydrogen and 95% of nitrogen, for example, at aspecified temperature for a specified period of time (e.g. at 800 to1400° C. for two hours). Thereafter, the baked powders are classified toprovide a desired blue phosphor, Ca_(1−x)MgSi₂O₆:Eu_(x).

The phosphor particles obtained by the hydrothermal synthesis or theatomization synthesis have a spherical shape and an average particlediameter ranging from 0.05 to 3.0 μm, which is smaller than that ofparticles fabricated by the conventional solid phase reaction method.The wording “spherical shape” used here is defined so that the aspectratios (minor axis diameter/major axis diameter) of most of the phosphorparticles range, for example, from 0.9 to 1.0; however, not all thephosphor particles need to be within the range.

Now will be described the phosphor of (Sr, Ca)_(1−x)MgSi₂O₆:Eu_(x). Thephosphor differs from aforementioned Ca_(1−x)MgSi₂O₆:Eu_(x) only in thatthe element Sr substitutes for a part of the element Ca ofCa_(1−x)MgSi₂O₆:Eu_(x) (where, the ratio of Sr to Ca is 0.1-1 to 0-1).The materials used are described hereinafter.

First, the materials, i.e., strontium nitrate [Sr(NO₃)₂], magnesiumnitrate [Mg(NO₃)₃], silicon oxide [SiO₂]—colloidal silica, europiumnitrate [(NO₃)₂] are mixed with water so as to have the molar ratio of1−X:1:2:X (0.03≦X≦0.20). Next, the mixture, together with an alkaline(basic) solution, is put into a container with the application ofultrasonic waves and O₂—, (or O₃—) bubbling to make a sphericalhydrate(precursor hydrate). After being baked in the air at temperatures800 to 1,450° C., the hydrate is further baked at 1000 to 1400° C. in areducing atmosphere, and then the particles are classified. Through theprocesses above, the aqueous solution reaction method can provide adesired blue phosphor.

Next will be described another method of producing (Ca,Ba)_(1−x)MgSi₂O₆:Eu_(x).

First, the materials, i.e., calcium alkoxide [Ca(O.R)₂], barium alkoxide[Ba(O.R)₂], where, the ratio of Ca to Ba is 0-1 to 1-1, silicon alkoxide[Si(O.R)₄], europium alkoxide [Eu(O.R)₃]— where, R belongs to an alkylgroup, are mixed so as to have the molar ratio of 1−X:1:2:X(0.03≦X≦0.2). Next, the mixture is hydrolyzed by the addition of wateror alcohol to obtain a spherical precursor. The precursor is baked attemperatures ranging from 1000 to 1400° C. Next, the obtained particlesare baked in a reducing atmosphere, for example, containing 5% ofhydrogen and 95% of nitrogen, at a specified temperature for a specifiedperiod of time (e.g. at 1000 to 1400° C. for two hours). Thereafter,using an air classifier, the particles are classified to obtain a bluephosphor. In this way, the hydrolysis method can also provide a bluephosphor.

Next will be described a phosphor of Ba_(3(1−x))MgSi₂O₈:Eu_(x).

In a mixed solution fabrication process, materials, i.e., barium nitrate[Ba(NO₃)₂], magnesium nitrate [Mg(NO₃)₃], silicon oxide [SiO₂]—colloidalsilica, and europium nitrate [Eu(NO₃)₂] are mixed in a molar ratio ofBa(NO₃)₂:Mg(NO₃)₃:SiO₂:Eu(NO₃)₂=3(1−X):1:2:X (0.003≦X≦0.20). Thismixture is dissolved in an aqueous medium to prepare a mixed solution.As for the aqueous medium, ion-exchange water or pure water ispreferably used by virtue of its containing no impurities; however, anaqueous medium containing non-aqueous solvent (e.g. methanol andethanol) can also be used.

Next, add an alkaline (basic) solution, such as potassium hydrate, tothe hydrate mixed solution prepared above to produce ahydrate(precursor) having spherical particles. After that, put thehydrate into a container made of a corrosion- and heat-resistantmaterial, such as gold and platinum. Then, the hydrate ishydro-thermally synthesized in a high pressure vessel, using equipmentcapable of heating and pressurizing at the same time, such as anautoclave, at specified temperatures (100 to 300° C.) under specifiedpressures (0.2 to 10 MPa). In this case, an aluminum powder or agraphite powder is used as a reducer for the blue phosphor. Thehydrothermal synthesis is thus carried out for 12 to 20 hours to obtaina spherical precursor.

Other than the aforementioned method with the use of autoclave pressure,a spray synthesis method can be used. In this case, the hydrate mixedsolution is directly fed from the pressure nozzle; the solution isultrasonically sprayed into a furnace heated at temperatures rangingfrom 1000 to 1500° C. to obtain the spherical precursor.

Next, the obtained precursor powder is baked in a reducing atmospherecontaining 5% of hydrogen and 95% of nitrogen, for example, at aspecified temperature for a specified period of time (e.g. at 800 to1400° C. for two hours). Thereafter, the baked powders are classified toprovide a desired blue phosphor, Ba_(3(1−x))MgSi₂O₈:Eu_(x).

The phosphor particles obtained by the hydrothermal synthesis or theatomization synthesis have a spherical shape and an average particlediameter ranging from 0.05 to 3.0 μm, which is smaller than that ofparticles fabricated by the conventional solid phase reaction method.The wording “spherical shape” used here is defined so that the aspectratios (minor axis diameter/major axis diameter) of most of the phosphorparticles range, for example, from 0.9 to 1.0; however, not all thephosphor particles need to have the range.

Now will be described a phosphor of (Ba, Sr)_(3(1−x))MgSi₂O₈:Eu_(x). Thephosphor differs from aforementioned Ba_(3(1−x))MgSi₂O₈:Eu_(x) in onlythat the element Sr substitutes for a part of the element Ba ofBa_(3(1−x))MgSi₂O₈:Eu_(x) (where, the ratio of Ba to Sr is 0.1-1 to0-1). The materials used are described hereinafter.

First, the materials, i.e., strontium nitrate [Sr(NO₃)₂], barium nitrate[Ba(NO₃)₂], magnesium nitrate [Mg(NO₃)₃], silicon oxide [SiO₂]—colloidalsilica, europium nitrate [(NO₃)₂] are mixed with water so as to have themolar ratio of 3(1−X):1:2:X (0.003≦X≦0.20). Next, the mixture, togetherwith an alkaline (basic) solution, is put into a container with theapplication of ultrasonic waves and O₂— (or O₃—) bubbling to make aspherical hydrate(precursor hydrate). After being baked in the air attemperatures 800 to 1450° C., the hydrate is further baked at 1000 to1400° C. in a reducing atmosphere, and then the particles areclassified. Through the processes above, the aqueous solution reactionmethod can provide a desired blue phosphor.

Next will be described another method of producing (Ca,Ba)_(1−x)MgSi₂O₆:Eu_(x).

First, the materials, i.e., calcium alkoxide [Ca(O.R)₂], barium alkoxide[Ba(O.R)₂], where, the ratio of Ca to Ba is 0-1 to 1-1, silicon alkoxide[Si(O.R)₄], europium alkoxide [Eu(O.R)₃]—where, R belongs to an alkylgroup, are mixed so as to have the molar ratio of 3(1−X):1:2:X(0.003≦X≦0.2). Next, the mixture is hydrolyzed by the addition of wateror alcohol to obtain a spherical precursor. The precursor is baked attemperatures ranging from 1000 to 1400° C. Next, the obtained particlesare further baked in a reducing atmosphere containing, for example, 5%of hydrogen and 95% of nitrogen, at a specified temperature for aspecified period of time (e.g. at 1000 to 1400° C. for two hours).Thereafter, using an air classifier, the particles are classified toobtain a blue phosphor. In this way, the hydrolysis method can alsoprovide a blue phosphor.

(2) Green Phosphor

First, a phosphor of Zn_(2(1−x))SiO₄:Mn_(x) is described. In a mixedsolution fabrication process, materials, i.e., zinc nitrate [Zn(NO₃)],colloidal silica [SiO₂], and manganese nitrate [Mn(NO₃)₂] are mixed in amolar ratio of Zn(NO₃):SiO₂:Mn(NO₃)₂=2−X:1:X (0.01≦X≦0.10). This mixtureis dissolved in ion-exchange water to prepare a mixed solution. Next, ina hydrate producing process, add alkaline solution (e.g. ammonia aqueoussolution) is added to the mixed solution to prepare a hydrate.

Thereafter, in a hydrothermal synthesis process, the hydrate and theion-exchange water are put into a capsule made of a corrosion- andheat-resistant material, such as gold and platinum. Then, the capsulecontaining the mixed solution is put into a high-pressure vessel toundergo hydrothermal synthesis. The hydrothermal synthesis process goeson for 2 to 10 hours at specified temperatures (100 to 300° C.) underspecified pressures (0.2 to 10 MPa), for example, with autoclavepressure being applied. The hydro-thermally synthesized particles aredried to obtain a desired phosphor of Zn_(2(1−x))SiO₄:Mn_(x). Thephosphor particle obtained by hydrothermal synthesis has a sphericalshape and an average particle diameter ranging from approx. 0.1 to 2.0μm. The phosphor particles are annealed in the air at temperaturesranging from 800 to 1100° C. and then classified. The green phosphorpowder is thus obtained.

Next will be described a phosphor of Ba_(1−x)Al₁₂O₁₉:Mn_(x). In a mixedsolution fabrication process, materials, i.e., barium nitrate[Ba(NO₃)₂], aluminum nitrate [Al(NO₃)₂], and manganese nitrate[Mn(NO₃)₂] are mixed in a molar ratio ofBa(No₃):Al(NO₃)₂:Mn(NO₃)₂=1−X:12:X (0.01≦X≦0.10). This mixture isdissolved in ion-exchange water to prepare a mixed solution.

Next, in a hydrate producing process, alkaline solution (e.g. ammoniaaqueous solution) is dropped into the mixed solution to prepare ahydrate. Thereafter, in a hydrothermal synthesis process, the hydrateand the ion-exchange water are put into a capsule made of a corrosion-and heat-resistant material, such as gold and platinum. Then, thecapsule containing the mixed solution is put into a high-pressure vesselto undergo hydrothermal synthesis. The hydrothermal synthesis processgoes on for 2 to 20 hours at specified temperatures (100 to 300° C.)under specified pressures (0.2 to 10 MPa), for example, with autoclavepressure being applied.

The hydro-thermally synthesized particles are dried to obtain a desiredphosphor of Ba_(1−x)Al₁₂O₁₉:Mn_(x). The phosphor particle obtained byhydrothermal synthesis has a spherical shape and an average particlediameter ranging from approx. 0.1 to 2.0 μm. The phosphor particles areannealed in the air at temperatures ranging from 800 to 1100° C. andthen classified. The green phosphor powder is thus obtained.

(3) Red Phosphor

First, a phosphor of (Y, Gd)_(1−x)BO₃:Eu_(x) is described.

In a mixed solution fabrication process, materials, i.e., yttriumhydroxide [Y₂(OH)₃], gadolinium hydroxide [Gd₂(OH)₃], boric acid[H₃BO₃], and europium hydroxide [Eu₂(OH)₃] are mixed in a molar ratio of[Y₂(OH)₃, Gd₂(OH)₃]:H₃BO₃:Eu₂(OH)₃=1−X:2:X (0.05≦X≦0.20), having a 65 to35 Y to Gd ratio. The mixture is dissolved in ion-exchange water toprepare a mixed solution. Next, in a hydration process, an aqueous base,such as ammonia aqueous solution, is added to the mixed solution toprovide a hydrate.

After that, in a hydrothermal synthesis process, the hydrate and theion-exchange water are put into a container made of a corrosion- andheat-resistant material, such as gold and platinum. Then, the containerhaving the mixed solution is put into a high-pressure vessel to undergohydrothermal synthesis. The hydrothermal synthesis takes place for 3 to12 hours at specified temperatures (100 to 300° C.) under specifiedpressures (0.2 to 10 MPa), for example, with autoclave pressure beingapplied. The phosphor particle obtained by hydrothermal synthesis has aspherical shape and an average particle diameter ranging from approx.0.1 to 2.0 μm. The phosphor is heated for two hours in the air attemperatures ranging from 800 to 1200° C. and then classified. A redphosphor is thus obtained.

Next, a description of Y_(2−x)O₃:Eu_(x) is provided. In a mixed solutionfabrication process, materials, i.e., yttrium nitrate [Y₂(NO₃)₂] andeuropium nitrate [Eu(NO₃)₂] are mixed in a molar ratio ofY₂(NO₃)₂:Eu(NO₃)₂=2−X:X (0.05≦X≦0.30). The mixture is dissolved inion-exchange water to prepare a mixed solution. Next, in a hydrationprocess, an aqueous base, such as ammonia aqueous solution, is added tothe mixed solution to provide a hydrate.

After that, in a hydrothermal synthesis process, the hydrate and theion-exchange water are put into a container made of a corrosion- andheat-resistant material, such as gold and platinum. Then, the containerhaving the mixed solution is put into a high-pressure vessel to undergohydrothermal synthesis. The hydrothermal synthesis takes place for 3 to12 hours at specified temperatures (100 to 300° C.) under specifiedpressures (0.2 to 10 MPa), for example, with the application ofautoclave pressure. The compound obtained by hydrothermal synthesis isdried to obtain a desired phosphor of Y_(2−x)O₃:Eu_(x).

Next, the phosphor particles are annealed in the air at temperaturesranging from 800 to 1200° C. and then classified. The red phosphorpowder is thus obtained. The phosphor obtained by the hydrothermalsynthesis process has a spherical shape and particle diameters rangingfrom approx. 0.1 to 2.0 μm. Such a shape and a size are suitable forforming a phosphor layer that exhibits excellent light emissioncharacteristics.

The phosphor particles described in (1) through (3) are produced by ahydrothermal synthesis method, atomization synthesis method, orhydrolysis method, using a spherical precursor prepared in an aqueoussolution. This is why a particle has a spherical shape and a smallaverage particle diameter (of approx. 0.1 to 2.0 μm). The phosphorobtained through the synthesis method above has no oxygen vacancy on itssurface of the particle, whereby not only luminance of the phosphor butalso luminance degradation is significantly improved. Besides,ultraviolet light penetrates not so far from the surface of the phosphorparticle: approx. several hundreds nm. That is, emission occurs almostat the surface. Considering that fact, 2.0 μm or smaller particlediameter increases the surface area of a particle contributing toemission. This allows the phosphor layers to maintain high luminance.

As another advantage, the phosphor particle produced through thesynthesis methods above sustains crystal growth with the spherical shapekept, so that the particle has fewer structural defects including theoxygen vacancy. Accordingly, ultraviolet light absorbed in the oxygenvacancy decreases, on the other hand, excitation at a mainly emittingelement easily occurs. In addition, the spherical shape of the particlecontributes to avoid each particle from sticking together in the bakingprocess at high temperatures, whereby the particle can be easilycrushed. The particle with fewer oxygen vacancy can not only providehigh luminance, but also minimize luminance degradation caused by theoxygen vacancy. The phosphor of the present invention can have aparticle diameter on the order of sub-microns, thereby minimizinginconsistencies in coating when the phosphor is applied. In addition, apacking factor of the phosphor forming a phosphor layer increases;accordingly, the PDP of the present invention has a higher luminancethan that of a conventional one.

In the description above, hydro-thermally synthesized phosphor particlesare employed for all the phosphor layers, which are responsible for redand green emission. An aqueous solution reaction method or atomizationsynthesis method can provide red-, and green-phosphor layers almost thesame as those obtained by the hydrothermal synthesis method.

Among the three colors of R, G, and B, especially the conventional bluephosphor of CaMgSi₂O₆:Eu has a lower luminance and noticeable luminancedegradation in the discharge. The inconvenience has contributed todecrease in the color temperature of white when the cells of threecolors emit light at the same time. For this reason, in a PDP, the colortemperature of white display has been improved, using circuits, byinefficiently decreasing the luminance of other phosphor cells(responsible for red and green emission) in line with the luminance ofthe blue emitting cells. However, using the blue phosphor produced bythe methods of the present invention, namely, the blue phosphor havingthe crystal structure of MeMgSi₂O₆:Eu or Me₃Si₂O₈:Eu (where, Me isformed of at least one of Ca, Sr, and Ba) can increase the luminance ofthe blue emitting cells. This eliminates the need of intentionallydecreasing the luminance of the cells of other colors.

Thus, the cells of all the colors no longer have an inefficient decreasein luminance. That is, making full use of the luminance of each cell canimprove luminance as a whole of a PDP, with the color temperature ofwhite display highly maintained. Furthermore, the blue phosphor of thepresent invention can be applied to fluorescent lighting that is excitedby ultraviolet light to emit light in a similar manner. Instead of theconventional blue phosphor applied to the inner wall of a fluorescenttube, the blue phosphor obtained by the methods of the invention: anaqueous solution reaction method; a hydrothermal synthesis method; and aspray synthesis method, can be employed for the tube. This replacementcan provide fluorescent lighting with improvement in luminance andluminance degradation.

Evaluation Experiment 1

In order to evaluate the performance of a plasma display device of thepresent invention, samples based on the aforementioned embodiment wereproduced to carry out performance evaluation tests. The experimentalresults are described below.

Each of the plasma display devices produced has a diagonal size of 42in.—for a high definition (HD) TV screen having a rib-pitch of 150 μm.Each of the PDP was produced so that the dielectric glass layer was 20μm thick; the MgO protective layer was 0.5 μm thick; and the distancebetween the display electrode and the display scan electrode was 0.08mm. The discharge space was filled with a discharge gas in which 5% ofxenon gas was mixed with neon as the major component. The discharge gaswas sealed in the discharge space with the application of specifieddischarging gas pressure of, for example, 73 kPa.

For all the phosphor particles used for PDPs of samples 1 through 9, aspherical-shaped precursor, which was prepared in an aqueous solution,was employed. Each phosphor was produced with the spherical precursorthat was obtained through an aqueous solution reaction method, ahydrothermal synthesis method, a spray synthesis method, or hydrolysismethod. Table 1 shows each data for synthesis of the samples.

TABLE 1 Blue Phosphor Red Phosphor Green Phosphor[Me_(1-x)MgSi₂O₆:Eu_(x)] [(Y,Gd)_(1-x)BO₃:Eu_(x)][(Zn_(1-x)Mn_(x))₂SiO₄] Sample Amount Manufacturing Material Ca/Sr/Amount Manufacturing Amount Manufacturing No. of Eu X method for Me Baratio of Eu X method of Eu X method 1 0.03 Hydrothermal Ca 1.0 0.1Hydrothermal 0.01 Hydrothermal synthesis synthesis synthesis methodmethod method 2 0.05 Hydrolysis Ca/Sr   1/0.1 0.2 Hydrothermal 0.02Hydrothermal method synthesis synthesis method method 3 0.1 Spray methodCa/Ba   1/0.1 0.3 Hydrothermal 0.05 Hydrothermal synthesis synthesismethod method 4 0.2 Aqueous Ca/Ba   1/0.5 0.15 Hydrothermal 0.1Hydrothermal solution synthesis synthesis reaction method method methodBlue Phosphor Red Phosphor Green Phosphor [Me_(1-x)MgSi₂O₆:Eu_(x)][(Y_(1-x))₂BO₃:Eu_(x)] [Ba_(1-x)Al₁₂O₁₉:Mn_(x)] 5 0.03 Aqueous Ca/Ba  1/0.5 0.01 Hydrothermal 0.01 Hydrothermal solution synthesis synthesisreaction method method method 6 0.1 Hydrothermal Ca/Sr/Ba 1/1/1 0.1Hydrothermal 0.02 Hydrothermal synthesis synthesis synthesis methodmethod method 7 0.1 Spray method Sr 1.0 0.15 Hydrothermal 0.05Hydrothermal synthesis synthesis method method 8 0.2 Hydrolysis Ba 1.00.2 Hydrothermal 0.1 Hydrothermal method synthesis synthesis methodmethod 9 0.2 Hydrolysis Sr/Ca   1/0.5 0.2 Hydrothermal 0.1 Hydrothermalmethod synthesis synthesis method method 10* 0.1 Solid-phase Ca 1.0 0.15Hydrothermal 0.01 Hydrothermal reaction synthesis synthesis methodmethod method 11* BaMgAl₁₀ Solid-phase — — 0.15 Hydrothermal 0.01Hydrothermal O₁₇:Eu reaction synthesis synthesis method Eu_(0.1) methodmethod *Sample Nos. 10 and 11 show comparative samples

Samples 1 through 4 are similarly structured so as to have a combinationof red phosphor of (Y, Gd)_(1−x)BO₃:Eu_(x), the green phosphor ofZn_(2−x)SiO₄:Mn_(x), and the blue phosphor of Me_(1−x)MgSi₂O₆:Eu_(x)(where, Me is a combination of Ca, Sr, and Ba). As shown in Table, 1these samples differ from each other in: manufacturing methods of thephosphor, the substitution ratios of Eu and Mn that serve as a mainemitter, i.e., the substitution ratios of Eu to the elements Y and Me,the substitution ratios of Mn to the element Zn, and a structuralcombination of Me.

Samples 5 through 9 are similarly structured so as to have a combinationof red phosphor of Y_(2−x)O₃:Eu_(x), the green phosphor ofBa_(1−x)Al₁₂O₁₉:Mn_(x), and the blue phosphor of Me_(1−x)MgSi₂O₆:Eu_(x)(where, Me is a combination of Ca, Sr, and Ba). As is the case ofsamples 1 through 4, the phosphors of these samples are manufactured bydifferent way: a hydrothermal synthesis method, a spray synthesismethod, and a hydrolysis method. The substitution ratios of the mainlyemitting element, and the structural combination of Me are changed asshown in Table 1. In addition, phosphor ink used for forming phosphorlayers is prepared by using each kind of phosphor particles shown inTable 1, and mixing the phosphor, resin, solvent and dispersant, withthe mixing ratio shown in the aforementioned description.

Samples 10 and 11 are comparative examples. In the two examples, the redphosphor of (Y, Gd)_(1−x)BO₃:Eu₂, and the green phosphor ofZn₂SiO₄:Mn_(x) are commonly manufactured by the hydrothermal synthesismethod. Samples 10 and 11 have differently structured blue phosphor;sample 10 employs the blue phosphor of CaMgSi₂O₆:Eu obtained by thesolid-phase reaction method, while sample 11 employs the blue phosphorof BaMgAl₁₀O₁₇:Eu, which is also produced by the solid-phase reactionmethod. With such structured samples 10 and 11, each phosphor layer isformed under the conditions similar to samples 1 through 9.

According to the measurement results, viscosity of each kind of thephosphor ink (at 25° C.) is kept within the range of 1500 to 30000 CP.Observations on each phosphor layer found that the phosphor ink isuniformly applied to the side faces of the barrier ribs. As for thephosphor particles used for phosphor layers of each color, thestructures and the manufacturing methods shown in Table 1 are used ineach sample.

As for the blue phosphor particles for samples 10 and 11, phosphorparticles undergo the solid phase reaction through the conventionalsintering process. With a ball grinder, the sintered phosphor particlesare crushed then classified to obtain the blue phosphor particles. Thered phosphor for samples 10 and 11 has the structure and themanufacturing method the same as those of sample 9: hydro-thermallysynthesized Y₂O₃:Eu (see Table 3). The particle has a spherical shapeand 2.0-μm particle diameter. Using the particles, a red phosphor layerformed has a film thickness of 20 μm. The green phosphor for samples 10,11 also has the structure and the manufacturing method the same as thoseof sample 9: hydro-thermally synthesized Ba_(1−x)Al₁₂O₁₉:Mn_(x). Theparticles obtained have 2.2-μm particle diameter, but are differentlysized. Using the particles, a green phosphor layer formed has a filmthickness of 20 μm. As for the blue phosphor, conventionally sinteredCaMgSi₂O₆:Eu is baked at 1400° C. in a H₂—N₂ gas. After 5-hour baking,the particles are crushed then classified so as to obtain a particlediameter of 4.0 μm.

Phosphor ink used for forming phosphor layers was prepared by using eachkind of phosphor particle shown in Table 1, and mixing the phosphor,resin, solvent and dispersant.

Measurements in some stages in manufacturing PDP were performed onsamples 1 through 9 and comparative samples 10, 11. These are: theluminance degradation factor of each phosphor when the phosphor is baked(at 520° C. in the air) in the rear panel manufacturing process; theluminance degradation factor of each phosphor in the panel sealingprocess with the application of heat at 450° C.; the luminancedegradation factor in a lifetime-accelerated test; the presence orabsence of addressing failure at address discharge; and the luminancewhen all the blue emitting cells turn ON.

To measure the luminance of the PDP, discharge sustain pulses at avoltage of 150V and at a frequency of 30 kHz were applied to the panel.

The evaluation on the luminance degradation factor was carried out asfollows. Discharge sustain pulses at a voltage of 200V and at afrequency of 100 kHz were applied to each sample PDP continuously for100 hours, and luminance of each PDP was measured before and after theapplication of the pulses. Based on the measurements, the luminancedegradation factor was derived from the expression of ((luminance afterpulse-application−luminance before pulse-application)/luminance beforepulse-application)*100.

Addressing failure at address discharge was determined by existence offlickers in an image. If a sample PDP has flickers in any one position,the PDP was judged as having flickers. As for the luminance distributionof each PDP, luminance at white display was measured with a luminancemeter, the distribution on the entire surface was shown.

Listed in Table 2 are the results on luminance and the luminancedegradation factors of each color. In the experiment, the discharge wasuniformly applied to each phosphor layer. The luminance suppressing ofred and green cells to control the color temperature of white displaywas not carried out.

TABLE 2 Luminance Luminance degradation factor Luminance degradationfactor (%) (%) of phosphor degradation factor of phosphor after theLuminance baked (520° C.) in (%) of phosphor when application of at bluerear panel panels are sealed discharge sustain Addressing display onmanufacturing (450° C.) in panel pulses (200 V, 100 kHz) failure at theentire Sample process sealing process for 100 hrs. address surface No.Blue Red Green Blue Red Green Blue Red Green discharge (cd/cm²) 1 −2.8−1.6 −4.5 −5.0 −2.4 −12.8 −0.9 −5.0 −14.0 None 81 2 −1.2 −1.4 −4.2 −1.3−2.1 −13.1 −0.6 −4.4 −14.8 None 84.6 3 −1.2 −1.8 −4.5 −1.4 −2.2 −13.0−0.7 −4.3 −14.2 None 87 4 −0.5 −1.3 −4.6 −1.3 −2.4 −12.8 −0.5 −4.2 −14.3None 88.1 5 −0.4 −1.5 −4.9 −0.4 −2.1 −13.1 −0.3 −4.3 −14.8 None 88.8 6−0.2 −1.2 −4.4 −0.3 −2.3 −12.8 −0.2 −4.1 −14.9 None 91.5 7 −1.4 −1.4−4.8 −1.1 −2.4 −12.6 −0.5 −4.3 −14.6 None 91 8 −1.3 −1.3 −4.4 −1.5 −2.6−12.9 −0.5 −4.8 −15.1 None 88.7 9 −0.4 −1.5 −4.1 −1.2 −2.4 −12.9 −0.7−4.4 −15.6 None 92.6 10* −4.6 −1.3 −4.2 −14.5 −2.3 −13.0 −11.0 −4.2−14.4 Exist 61 11* −5.6 −1.5 −4.1 −21.8 −2.4 −13.2 −34.6 −4.1 −15.6Exist 46 *Sample Nos. 10 and 11 show comparative samples

As shown in Table 2, in comparative samples 10 and 11, the luminancedegradation factors of the conventional blue phosphor baked at 520° C.are −4.6% (sample 10) and −5.6% (sample 11); the luminance degradationfactors in the panel sealing process (at 450° C.) are −14.5% (sample 10)and −21.8% (sample 11); and the luminance changes after application ofthe discharge sustain pulse for 100 hours are −11.0% (sample 10) and−34.6% (sample 11). Addressing failure was observed in both samples. Asfor luminance of the blue color of the PDP, samples 10 and 11 had dataresulted in 61 cd/cm², 46 cd/cm², respectively.

On the other hand, in samples 1 through 9, which employ the bluephosphor formed of Me_(1−x)MgSi₂O₆:Eu_(x), the luminance with all theblue emitting cells turned ON exceeded 80 cd/cm² for all the samples.Furthermore, the luminance degradation factors in the phosphor-bakingprocess (at 520° C.) ranged from −0.2% to −2.8%; the luminancedegradation factors in the panel sealing process (at 450° C.) rangedfrom −0.3% to −0.5%; and the luminance changes after application of thedischarge sustain pulse for 100 hours achieved −0.2 to −0.9% range. Noaddressing failure was observed.

It is apparent from the results that the PDP device of the presentinvention is superior to comparative samples 10 and 11 in the luminanceof a panel, the luminance degradation factors in the manufacturingprocesses, and addressing failure of the discharge.

This is because the blue phosphor particle of the present invention hasa crystal structure of Me_(1−x)MgSi₂O₆:Eu_(x) (where, Me is formed of atleast one of Ca, Sr, and Ba) processed by an aqueous solution reactionsynthesis method, a hydrothermal synthesis method, a spray synthesismethod, or a hydrolysis method. With the crystal structure and thesynthesis methods above, a phosphor particle with a relatively small(ranging from 0.1 to 3.0 μm) size and a generally spherical shape isobtained. Such a small, spherical particle has no need to be crushed,and can suppress undesired oxygen vacancy. At the same time, the packingfactor of the phosphor particles in a phosphor layer increases,accordingly, the surface area of the phosphor particles that contributeto emission increases. A panel having a blue phosphor in which theamount of Ca is partly or completely replaced with a mixture of Ca andBa can provide a noticeable improvement in luminance and characteristicsrather than a panel having a blue phosphor that consists of Ca.

As described above, the occurrence of the oxygen vacancy is suppressedin the blue phosphor particles, which prevents the phosphor particlefrom low crystal growth that develops from where the oxygen vacancyoccurs. The low occurrence of the oxygen vacancy noticeably contributesto suppressing degradation in the color temperature of blue and theluminance. At the same time, the lower the occurrence of the oxygenvacancy is, the lower the amount of ultraviolet light is absorbed intothe oxygen vacancy. This fact encourages excitation of an element thatmainly emits light, providing improved luminance higher than theconventional blue phosphor.

Evaluation Experiment 2

In experiment 1, the phosphors of the present invention were used forPDPs. Samples of fluorescent lighting using the phosphor of the presentinvention were prepared for fluorescent lighting that is excited byultraviolet light to emit light in a similar manner.

To provide fluorescent lighting sample 12, phosphors of each colorproduced under the condition of sample 4 in Table 1 were mixed and themixture was applied to the inner wall of a glass tube, as a phosphorlayer of known fluorescent lighting. As a comparative example thereof,phosphors of each color produced by a conventional solid phase reactionmethod under the condition of sample 11 (in Table 1) were also mixed andthe mixture was applied to form a phosphor layer. Fluorescent lightingcomparative sample 13 was thus prepared.

An evaluation performed on the aforementioned samples 12 and 13 wascarried out as follows. Pulse voltage of 100V-60 Hz was applied to eachsample for 5000 hours, and luminance of each sample was measured beforeand after the application of the pulse voltage. Based on themeasurements, the luminance degradation factor was derived from theexpression of ((luminance after pulse-application−luminance beforepulse-application)/luminance before pulse-application)*100. Table 3shows the results.

TABLE 3 Luminance degradation Luminance after 5000 hours Sample No.Phosphor (cd/m²) (100 V, 60 Hz) 12 Phosphor of 6880 −0.30% Sample No. 7 13* Phosphor of 6600 −14.6% Sample No. 11 *Sample No. 13 showscomparative samples

Compared to fluorescent lighting sample 13, as shown in Table 3,fluorescent lighting sample 12—which employs the blue phosphor particlewith a Me_(1−x)MgSi₂O₆:Eu_(x)—structure produced by, for example, aspray synthesis method, a hydrothermal synthesis method, or a hydrolysismethod, using a spherical precursor obtained in an aqueous solution—notonly has approx. 4% of improvement in luminance, but also can desirablyattenuate luminance degradation.

Evaluation Experiment 3

Next, another evaluation experiment was carried out on a plasma displaydevice employing the phosphor havingMe_(3(1−x))MgSi₂O₈:Eu_(x)-structure. Like aforementioned experiment 1,the evaluation was performed on samples. Table 4 shows the experimentresults.

TABLE 4 Blue Phosphor [Me_(3(1-x))MgSi₂O₆:Eu_(x)] Red Phosphor GreenPhosphor Precursor- [(Y,Gd)_(1-x)BO₃:Eu_(x)] [(Zn_(1-x)Mn_(x))₂SiO₄]Sample Amount manufacturing Material Ca/Sr/ Amount Manufacturing AmountManufacturing No. of Eu X method for Me Ba ratio of Eu X method of Eu Xmethod 1 0.03 Hydrothermal Ba 1.0 0.1 Hydrothermal 0.01 Hydrothermalsynthesis synthesis synthesis method method method 2 0.05 HydrolysisBa/Sr   1/0.1 0.2 Hydrothermal 0.02 Hydrothermal method synthesissynthesis method method 3 0.1 Spray method Ba/Sr 0.1/0.1 0.3Hydrothermal 0.05 Hydrothermal synthesis synthesis method method 4 0.2Aqueous Ba/Ca   1/0.5 0.15 Hydrothermal 0.1 Hydrothermal solutionsynthesis synthesis reaction method method method Blue Phosphor RedPhosphor Green Phosphor [Me_(3(1-x))MgSi₂O₈:Eu_(x)][(Y_(2-x))₂O₃:Eu_(x)] [Ba_(1-x)Al₁₂O₁₉:Mn_(x)] 5 0.003 Aqueous Ca/Ba  1/0.5 0.01 Hydrothermal 0.01 Hydrothermal solution synthesis synthesisreaction method method method 6 0.1 Hydrothermal Ca/Sr/Ba 1/1/1 0.1Hydrothermal 0.02 Hydrothermal synthesis synthesis synthesis methodmethod method 7 0.1 Spray method Sr 1.0 0.15 Hydrothermal 0.05Hydrothermal synthesis synthesis method method 8 0.2 Hydrolysis Ca 1.00.2 Hydrothermal 0.1 Hydrothermal method synthesis synthesis methodmethod 9 0.2 Hydrolysis Sr/Ca   1/0.5 0.2 Hydrothermal 0.1 Hydrothermalmethod synthesis synthesis method method 10* 0.1 Solid-phase Ba 1.0 0.15Hydrothermal 0.01 Hydrothermal reaction synthesis synthesis methodmethod method 11* 0.1 Solid-phase BaMgAl₁₀ — 0.15 Hydrothermal 0.01Hydrothermal reaction O₁₇:Eu synthesis synthesis method method method12* 0.1 Solid-phase CaMgSi₂ — 0.15 Hydrothermal 0.01 Hydrothermalreaction O₆:Eu synthesis synthesis method method method *Sample Nos. 10,11 and 12 show comparative samples

Samples 1 through 4 are similarly structured so as to have a combinationof red phosphor of (Y, Gd)_(1−x)BO₃:Eu_(x), the green phosphor ofZn_(2−x)SiO₄:Mn_(x), and the blue phosphor of Me_(3(1−x))MgSi₂O₈:Eu_(x)(where, Me is a combination of Ca, Sr, and Ba). As shown in Table 4,these samples differ from each other in: manufacturing methods of thephosphor, the substitution ratios of Eu and Mn that serve as a mainemitter, i.e., the substitution ratios of Eu to the elements Y and Me,the substitution ratios of Mn to the element Zn, and a structuralcombination of Me.

Samples 5 through 9 are similarly structured so as to have a combinationof red phosphor of Y_(2−x)O₃:Eu_(x), the green phosphor ofBa_(1−x)Al₁₂O₁₉:Mn_(x), and the blue phosphor ofMe_(3(1−x))MgSi₂O₈:Eu_(x) (where, Me is a combination of Ca, Sr, andBa). As is the case of samples 1 through 4, the phosphors of thesesamples are manufactured by different way: a hydrothermal synthesismethod, a spray synthesis method, and a hydrolysis method. Thesubstitution ratios of the mainly emitting element, and the structuralcombination of Me are changed as shown in Table 4. In addition, phosphorink used for forming phosphor layers was prepared by using each kind ofphosphor particle shown in Table 4, and mixing the phosphor, resin,solvent and dispersant, with the mixing ratio shown in the table.

Samples 10, 11 and 12 are comparative examples. In the three examples,the red phosphor of (Y_(1−x))₂O₃:Eu₂, and the green phosphor ofBa_(1−x)Al₁₂O₁₉:Mn_(x) are manufactured by the hydrothermal synthesismethod. Samples 10, 11 and 12 have differently structured blue phosphor;sample 10 employs a blue phosphor of Ba₃MgSi₂O₈:Eu, sample 11 employs ablue phosphor of BaMgAl₁₀O₁₇:Eu, and sample 12 employs a blue phosphorof CaMgSi₂O₆:Eu. All of which are produced by the solid phase reactionmethod. With such structured samples 10, 11 and 12, each phosphor layeris formed under the conditions similar to samples 1 through 9.

According to the measurement results, viscosity of each kind of thephosphor ink (at 25° C.) is kept within the range of 1500 to 30000 CP.Observations on each phosphor layer told that the phosphor ink wasuniformly applied to the side faces of the barrier ribs. As for thephosphor particles used for phosphor layers of each color, thestructures and the manufacturing methods shown in Table 4 are used ineach sample.

As for the blue phosphor particles for samples 10, 11 and 12, thephosphor particles undergo the solid phase reaction through theconventional sintering process. With a ball grinder, the sinteredphosphor particles are crushed then classified to obtain the bluephosphor particles. The red phosphor for samples 10, 11 and 12 has thestructure and the manufacturing method the same as those of sample 9:hydro-thermally synthesized Y₂O₃:Eu. The particle has a spherical shapeand 2.0-μm particle diameter. Using the particles, a red phosphor layerformed has a film thickness of 20 μm. The green phosphor for samples 10,11, and 12 also has the structure and the manufacturing method the sameas those of sample 9: hydro-thermally synthesizedBa_(1−x)Al₁₂O₁₉:Mn_(x). The particles obtained have 2.2-μm particlediameter, but are differently sized. Using the particles, a greenphosphor layer formed has a film thickness of 20 μm. As for the bluephosphor, conventionally sintered CaMgSi₂O₆:Eu (for sample 10);BaMgAl₁₀O₁₇:Eu (for sample 11); and CaMgSi₂O₆:Eu (for sample 12) arebaked at 1400° C. in a H₂—N₂ gas. After 5-hour baking, the particles arecrushed then classified so as to obtain a particle diameter of 4.0 μm.

Phosphor ink used for forming phosphor layers was prepared by using eachkind of phosphor particles shown in Table 4, and mixing the phosphor,resin, solvent and dispersant.

Measurements in some stages in manufacturing PDP were performed onsamples 1 through 9 and comparative samples 10, 11, 12. These are: theluminance degradation factor of each phosphor when the phosphor is baked(at 520° C. in the air) in the rear panel manufacturing process; theluminance degradation factor of each phosphor in the panel sealingprocess with the application of heat at 450° C.; the luminancedegradation factor in the lifetime-accelerated test; the presence orabsence of addressing failure at address discharge; and the luminancewhen all the blue emitting cells turns ON.

Listed in Table 5 are the results on luminance and the luminancedegradation factors of each color. In the experiment, the discharge wasuniformly applied to each phosphor layer. The luminance suppressing ofred and green cells to control the color temperature of white displaywas not carried out.

TABLE 5 Luminance Luminance degradation factor Luminance degradationfactor (%) (%) of phosphor degradation factor of phosphor after theLuminance baked (520° C.) in (%) of phosphor when application of at bluerear panel panels are sealed discharge sustain Addressing display onmanufacturing (450° C.) in panel pulses (200 V, 100 kHz) failure at theentire Sample process sealing process for 100 hrs. address surface No.Blue Red Green Blue Red Green Blue Red Green discharge (cd/cm²) 1 −1.8−1.6 −4.5 −3.0 −2.4 −12.8 −0.5 −5.0 −14.0 None 83 2 −1.0 −1.4 −4.2 −1.0−2.1 −13.1 −0.4 −4.4 −14.8 None 85.7 3 −1.1 −1.8 −4.5 −1.1 −2.2 −13.0−0.5 −4.3 −14.2 None 88.2 4 −0.4 −1.3 −4.6 −0.9 −2.4 −12.8 −0.4 −4.2−14.3 None 88.4 5 −0.3 −1.5 −4.9 −0.3 −2.1 −13.1 −0.2 −4.3 −14.8 None 896 −0.2 −1.2 −4.4 −0.2 −2.3 −12.8 −0.2 −4.1 −14.9 None 91.7 7 −1.1 −1.4−4.8 −1.0 −2.4 −12.6 −0.3 −4.3 −14.6 None 91.2 8 −1.3 −1.3 −4.4 −1.5−2.6 −12.9 −0.5 −4.8 −15.1 None 88.8 9 −0.4 −1.5 −4.1 −1.2 −2.4 −12.9−0.5 −4.4 −15.6 None 92.7 10* −3.6 −1.3 −4.2 −12.5 −2.3 −13.0 −10.5 −4.2−14.4 Exist 65 11* −5.6 −1.5 −4.1 −21.8 −2.4 −13.2 −34.6 −4.1 −15.6Exist 46 12* −4.6 −1.5 −4.1 −14.5 −2.4 −13.1 −11 −4.1 −15.5 Exist 61*Sample Nos. 10, 11 and 12 show comparative samples

As shown in Table 5, in comparative samples 10, 11 and 12, the luminancedegradation factors of the conventional blue phosphor baked at 520° C.are −3.6% (sample 10), −5.6% (sample 11), and −4.6% (sample 12); theluminance degradation factors in the panel sealing process (at 450° C.)are −12.5% (sample 10), −21.8% (sample 11), and −14.5% (sample 12); andthe luminance changes after application of the discharge sustain pulsefor 100 hours are −10.5% (sample 10), −34.6% (sample 11), and −11.0%(sample 12). Addressing failure was observed in all the samples. As forluminance of the blue color of the PDP, samples 10, 11 and 12 had dataresulted in 65 cd/cm², 46 cd/cm², and 61 cd/cm², respectively.

On the other hand, in samples 1 through 9, which employ the bluephosphor formed of Me_(3(1−x))MgSi₂O₈:Eu_(x), the luminance with all theblue emitting cells turned ON exceeded 83 cd/cm² in all the samples.Furthermore, the luminance degradation factors in the phosphor-bakingprocess (at 520° C.) ranged from −0.2% to −1.8%; the luminancedegradation factors in the panel sealing process (at 450° C.) rangedfrom −0.2% to −3.0%; and the luminance changes after application of thedischarge sustain pulse for 100 hours achieved −0.1 to −0.5% range. Noaddressing failure was observed.

It is apparent from the results that the PDP device of the presentinvention is superior to comparative samples 10, 11 and 12 in theluminance of a panel, the luminance degradation factors in themanufacturing processes, and addressing failure of the discharge.

This is because the blue phosphor particle of the present invention hasa crystal structure of Me_(3(1−x))MgSi₂O₈:Eu_(x) (where, Me is formed ofat least one of Ca, Sr, and Ba) processed by an aqueous solutionreaction synthesis method, a hydrothermal synthesis method, a spraysynthesis method, or a hydrolysis method. With the crystal structure andthe synthesis methods above, a phosphor particle with a relatively small(ranging from 0.1 to 3.0 μm) size and a generally spherical shape isobtained. Such a small, spherical particle has no need to be crushed,and can suppress undesired oxygen vacancy. At the same time, the packingfactor of the phosphor particles in a phosphor layer increases,accordingly, the surface area of the phosphor particles that contributeto emission increases. A panel having a blue phosphor in which theamount of Ba is partly or completely replaced with a mixture of Ca andSr can provide a noticeable improvement in luminance and characteristicsrather than a panel having a blue phosphor that consists of Ba.

As described above, the occurrence of the oxygen vacancy is suppressedin the blue phosphor particles, which prevents the phosphor particlefrom low crystal growth that develops from where the oxygen vacancyoccurs. The low occurrence of the oxygen vacancy noticeably contributesto suppressing degradation in the color temperature of blue and theluminance. At the same time, the lower the occurrence of the oxygenvacancy, the lower the amount of ultraviolet light absorbed into theoxygen vacancy. This fact encourages excitation of a mainly emittingelement, providing improved luminance higher than the conventional bluephosphor.

Evaluation Experiment 4

Using the phosphor evaluated in experiment 3, samples of fluorescentlighting were prepared for fluorescent lighting, which is excited byultraviolet light to emit light in a similar manner. As is the case withexperiment 2, to provide fluorescent lighting sample 12, phosphors ofeach color produced under the condition of sample 4 in Table 4 weremixed and the mixture was applied to the inner wall of a glass tube, asa phosphor layer of known fluorescent lighting. As a comparative examplethereof, phosphors of each color produced by a conventional solid phasereaction method under the condition of sample 11 (in Table 4) were alsomixed and the mixture was applied to form a phosphor layer. Fluorescentlighting comparative sample 13 was thus prepared.

An evaluation performed on the aforementioned samples 12 and 13 wascarried out as follows. Pulse voltage of 100V-60 Hz were applied to eachsample for 5000 hours, and luminance of each sample was measured beforeand after the application of the pulse voltage. Based on themeasurements, the luminance degradation factor was derived from theexpression of ((luminance after pulse-application−luminance beforepulse-application)/luminance before pulse-application)*100. Table 6shows the results.

TABLE 6 Luminance degradation Luminance after 5000 hours Sample No.Phosphor (cd/m²) (100 V, 60 Hz) 12 Phosphor of 6885 −0.30% Sample No. 7 13* Phosphor of 6600 −14.6% Sample No. 11 *Sample No. 13 showscomparative samples

Compared to fluorescent lighting sample 13, as shown in Table 6,fluorescent lighting sample 12—which employs the blue phosphor particlewith a Me_(3(1−x))MgSi₂O₈:Eu_(x)—structure produced by a spray synthesismethod, a hydrothermal synthesis method, or a hydrolysis method, using aspherical precursor obtained in an aqueous solution—not only has approx.4% of improvement in luminance, but also can desirably attenuateluminance degradation.

Industrial Applicability

According to the present invention, as described above, the bluephosphor particles have a structure formed of Me_(1−x)MgSi₂O₆:Eu_(x), orMe_(3(1−x))MgSi₂O₈:Eu_(x) (where, Me contains at least one of Ca, Sr,and Ba), which is produced by an aqueous solution reaction method, ahydrothermal synthesis method, or a spray synthesis method. Employingthe blue phosphor for a phosphor layer can enhance the absorption ofultraviolet light in the phosphor layer, thereby increasing luminance,the lifetime, and reliability of a plasma display device and a lightingdevice including a lamp.

List of the Reference Marks in the Drawings

-   100: PDP-   101: front glass substrate-   102: rear glass substrate-   103: display electrodes-   104: display scan electrodes-   105: dielectric glass-   106: MgO protective layer-   107: address electrodes-   108: dielectric glass layer-   109: barrier ribs-   110R: phosphor layer (Red)-   110G: phosphor layer (Green)-   110B: phosphor layer (Blue)-   122: discharge space

1. A method of manufacturing a phosphor of any one of MeMgSi₂O₆:Eu andMe₃MgSi₂O₈:Eu wherein Me comprises at least one of Ca, Sr, and Ba withan average diameter ranging from 0.1, to 3.0 μm, the method comprising:preparing a mixed solution by mixing a material and an aqueous medium;preparing a hydrate by mixing the mixed solution and an alkaline base;preparing a precursor by performing a hydrothermal synthesis reaction ona solution containing the hydrate and water therein at temperaturesranging from 100 to 300° C. under pressures ranging from 0.2 to 10 MPa;and baking the precursor at temperatures ranging from 800 to 1400° C. ina reducing atmosphere.
 2. A method of manufacturing a phosphor of anyone of MeMgSi₂O₆:Eu and Me₃MgSi₂O₈:Eu wherein Me comprises at least oneof Ca, Sr, and Ba with an average diameter ranging from 0.1 to 3.0 μm,the method comprising: preparing a mixed solution by mixing a materialand an aqueous medium; preparing a hydrate by putting the mixed solutionand an alkaline base into a container and then simultaneously applyingultrasonic wave and O₂—(or O₃—)bubbling to the container to obtain goodmixture; drying the hydrate and then baking the hydrate in an air attemperatures ranging from 800 to 1250° C.; and baking the hydrate in areducing atmosphere at temperatures ranging from 1000 to 1400° C.
 3. Amethod of manufacturing a phosphor of any one of MeMgSi₂O₆:Eu andMe₃MgSi₂O₈:Eu wherein Me comprises at least one of Ca, Sr, and Ba withan average diameter ranging from 0.1 to 3.0 μm, the method comprising:mixing alkoxide that contains Ca, Ba, Sr, Si, Mg, and Eu, with anaqueous medium; preparing a precursor hydrate for a blue phosphor bymixing the mixed solution with a simultaneous application of ultrasonicwave and O₂—(or O₃—)bubbling; drying the hydrate and then baking thehydrate in an air at temperatures ranging from 1000 to 1400° C.; andbaking the hydrate in a reducing atmosphere at temperatures ranging from1000 to 1400° C.